1. Field of the Invention
The present invention relates to an OLED display device and a method of manufacturing the same, the display that can maximize a resonance effect during an emission operation, thereby increasing luminous efficiency and color reproduction during a bottom emission operation.
2. Description of the Related Art
In general, an organic light emitting diode (OLED) display device can operate on the following principle. Electrons are injected from an electron injection electrode (or cathode) into an emission layer (EML), while holes are injected from a hole injection electrode (or anode) into the EML. The holes and electrons injected into the EML recombine in the EML to generate excitons. Thus, while the excitons are making the transition from an excited state to a ground state, the OLED display device can emit light. Based on the above-described principle and unlike a conventional liquid crystal display (LCD), the OLED display device requires no additional light source thereby reducing the volume and weight of a display device.
OLED display devices can be classified into a passive matrix (PM) type and an active matrix (AM) type depending on how the N×M pixels, which are arranged in a matrix shape, are driven. Although a PM OLED display device is configured using a simple fabrication process, the PM OLED display device can consume a lot of power and have technical limitations in implementing large-scaled display. Also, the PM OLED display device can have a lower aperture ratio and an increased number of interconnections.
In another aspect, OLED display devices can be categorized as a top-emitting type or a bottom-emitting type depending on a direction in which light is emitted from an organic EML. A bottom-emitting type OLED display device, which emits light toward a substrate, can adopt a reflective electrode or reflective layer together with a transparent electrode as an upper electrode and a transparent electrode as the lower electrode. In the case of an AM OLED display device using a thin film transistor (TFT), since light can not be transmitted through a portion where the TFT is located, the area of an emission unit can be reduced. In contrast, a top-emitting OLED display device, which emits light in a direction away from the substrate, can have a transparent electrode as an upper electrode and a reflective electrode and a transparent electrode as the lower electrode. Thus, an area through which light is transmitted can be increased, thereby improving the luminance of the OLED display device. Nowadays, more attention is being paid to a double-sided OLED display device capable of embodying a top-emitting type and a bottom-emitting type on a single substrate.
However, although a conventional OLED display device can be employed without any problem in a top-emitting mode, transmittance degradation due to an organic layer can preclude obtaining a high-quality image in a bottom-emitting mode.